1. Field of the Invention
The present invention relates to portable building structures, and more particularly, to uniformly tensioning panels of portable building structures.
2. Description of Related Art
The need for portable, inexpensive, and quickly erectable temporary building structures has led to the development of flexible, fabric covered, frame structures. These portable structures typically are insulated, and thus provide heating and cooling capability comparable to permanent building structures of wood, masonry, concrete or steel.
Portable building structures have been developed which include a plurality of transverse metal arches with individual flexible panels stretched between the metal arches. The panels are stretched by separating the arches and/or pulling transversely on the ends of the panels to form an enclosed area.
However, strength as well as aesthetic appearance is extremely important, for obvious reasons, when portable buildings are used for commercial purposes. Uniform tensioning of the panels causes the stress throughout the panels to be evenly distributed, thereby strengthening the entire structure. Further, uniform tensioning of the panels reduces or eliminates visible wrinkles in the stretched panels. Therefore, uniformly tensioned panels result in strong and appealing building structures and are highly desirable.
U.S. Pat. No. 5,146,722, issued on Sep. 15, 1992 to the present applicant, and incorporated by reference herein, discloses a fabric structure with double tensioning cables for accomplishing transverse stretching of fabric panels. The structure includes a plurality of cables forming large catenary arches, each having a lower end. Also, each lower end is attached to a respective base plate. The fabric panels are stretched between the large catenary arches while being held securely at the respective lower end by the respective base plate. However, although wrinkles are limited, it would be desirable to eliminate all wrinkles and to also have smaller catenary arches. Therefore, there is a need in the art for a method and apparatus for uniformly stretching and tightening all portions of the panels to eliminate wrinkles and to decrease the size of the catenary arches.